(i) Field of the Invention
This invention relates to a method for the containment of oil generated by an underwater oil (and gas) blowout of an offshore oil (and gas) well within an offshore oil-containment dome. It relates still further to a method for storing excess oil offshore in such dome.
(ii) Description of the Prior Art
In the event of a blowout from an offshore, underwater well, large quantities of oil and/or gas issue from the subsea location and this creates an environmental pollution problem. This is more acute in the Arctic. In the event of the presence of an ice cover over the blowout, any such oil will be spread below the ice under-surface and more or less be confined by the irregularities in this surface. A boom on the surface could confine most of this oil in open water but would have no effect below the ice. Should such submarine blowout occur, which the blowout prevention hardware of the producing well cannot stop, the standard procedure presently employed is to drill an angled hole to relieve the pressure. This procedure could take several weeks to complete.
Should a blowout of oil occur in the closing weeks of a summer drilling season in the Arctic, however, there might not be sufficient time to drill such relief well. Therefore, the oil blowout could be continuous through the entire freeze-up which averages 200 days per year. The ice in the Beaufort Sea area is in motion during the winter and a serious oil blowout could smear the bottom of the ice and the oil spread over a track of several thousand miles before any remedy could be effected for the blowout or any clean up commenced.
It is therefore desirable to provide a means for the containment of such oil blowout. One solution to such problem was provided by a device provided by one of the present applicants. Such device could be placed over an underwater oil and gas blowout to contain a large quantity of the oil to the vicinity of the plume where the oil can be burned, with such device being able to be placed over a blowout after it occurred. The device was disclosed and claimed in copending Canadian application Ser. No. 270,227 filed Jan. 21, 1977. By that application, a gas containment plume was provided by a device comprising a dome having a peripheral downwardly extending skirt; a central oil outlet tube, such tube having a inlet communication with a floating layer of sub-surface contained oil; means associated with the bottom of such skirt for anchoring such plume over the region of an underwater blowout; a plurality of peripherally disposed, spaced-apart gas outlet valves; and a central control system for operating such gas outlet valves.
That application also provided a method for containing and cleaning oil and gas blowouts from an undersea well by the steps of: (i) setting mooring points around a well location prior to drilling such well; (ii) if a blowout occurs, anchoring the above-described dome over such blowout using such mooring system; (iii) buoying up such dome on a layer of gas and oil under water above the blowout, such dome now being filled with gas; (iv) permitting gas to escape from the periphery of the dome to provide a containment torus on the surface of the water; (v) permitting oil to escape through such central oil outlet tube to the region of the containment torus; and (vi) igniting the gas and oil to clean the oil and gas blowout by continuous burning.
The dome described above in the above-identified Canadian patent application was anchored over the plume close to the sea bed and so was below the moving ice. The device first partially filled with oil and gas. The gas then escaped out through valves around the periphery of the device and formed a circular plume on the water surface which caused strong radially inward surface currents. The oil rose in the center of the gas containment plume (or partially within the gas plume) and so was confined.
However, the need still exists to provide such oil containment dome which could be positioned quickly over a blowout and hold the entire amount of oil and/or gas expelled during the blowout, to allow a controlled escape, if necessary, of the gas in the blowout, to have the collected oil pumped, if desired, into tankers the following summer, and to be removed from the blowout for use at future blowout locations.